A080199 a(1)=1; for n>1, a(n)=a(n-1) - 3 if n is already in the sequence, a(n)=a(n-1) + 6 otherwise.

1, 7, 13, 19, 25, 31, 28, 34, 40, 46, 52, 58, 55, 61, 67, 73, 79, 85, 82, 88, 94, 100, 106, 112, 109, 115, 121, 118, 124, 130, 127, 133, 139, 136, 142, 148, 154, 160, 166, 163, 169, 175, 181, 187, 193, 190, 196, 202, 208, 214, 220, 217, 223, 229

Offset: 1

Author

N. J. A. Sloane, Mar 20 2003

Keywords

• nonn

Links

• B. Cloitre, N. J. A. Sloane and M. J. Vandermast, Numerical analogues of Aronson's sequence, J. Integer Seqs., Vol. 6 (2003), #03.2.2.
• B. Cloitre, N. J. A. Sloane and M. J. Vandermast, Numerical analogues of Aronson's sequence (math.NT/0305308)

Crossrefs

Cf. A080455-A080458, A080036, A080037.

Programs

Mathematica

a[1] = 1;
a[n_] := a[n] = If[MemberQ[Array[a, n-1], n], a[n-1]-3, a[n-1]+6];
Array[a, 54] (* Jean-François Alcover, Feb 13 2019 *)

Formula

a(n) = 3*n*(1 + 1/log_3(n)) + o(n).